Re: where to write temporary files?

From:

"Tom Serface" <tom.nospam@camaswood.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 5 May 2008 16:37:46 -0700

Message-ID:

<B0BF6FD3-0C4E-4938-B69A-4A62901F82F0@microsoft.com>

Good points of course, but the ones I'm talking about are mostly just flat
files that need to be updated. I understand your point though and I agree.
I tend to use a database for data that changes dynamically and from multiple
sources. It's nice that you can even use something like SQL Server CE for
very small applications without my trouble.

Tom

"Joseph M. Newcomer" <newcomer@flounder.com> wrote in message
news:fbsu14l7qvm4h9okfuqr4tqraks80nkmde@4ax.com...

One of the problems that arises with this paradigm is how do you update a
file atomically,
that is, how do you insert or remove text from an existing file that might
be concurrently
accessed by some other process. In this case, there are too many
synchronization holes in
the copy-and-rename to work right, and the trick is to open the file in
exclusive mode,
create a memory mapping (extend the mapping if doing an insertion), do
in-memory moves
(memmove) to rearrange the contents, and then call SetFilePosition and
SetEndOfFile, to
update the information. That way there is no chance of concurrency
interfering. (I use
this example in my Systems Programming Course to show that memory-mapped
files are useful
for more than just doing a fancy interprocess shared memory segment).
joe